Question 53308
{{{f(x)25-x^2}}} 
This is the difference between two perfect squares.   
{{{a^2-b^2=(a+b)(a-b)}}}
In your case a=5 and b=x
{{{f(x)=25-x^2=(5+x)(5-x)}}}
Let f(x)=0
{{{0=(5+x)(5-x)}}}
Use the zero product property and set each parenthesis = 0.
5+x=0
-5+5+x=0-5
x=-5
and 
5-x=0
-5-x=0-5
-x=-5
-x/-1=-5/-1
x=5
Those are your x intersepts:(5,0),(-5,0).
Let x=0 and find your y intersept:
y=25-0^2
y=25
Now you can plot your y-intersept:(0,25)
This also happens to be the vertex of the parabola in this case.
The fact that x^2 is negative tells you that the parabola opens upside down.
{{{graph(300,200,-10,10,5,26,25-x^2)}}}